Crankshaft for two-stroke engines with twelve cylinders in line



J. STEIGER 2,426,753

CRANKSHAFT FOR TWO-STROKE ENGINES WITH TWELVE CYLINDERS IN LINE I Sept.- 2, 1947.

Fild Sept. 3, 1943 s Shee ts-Sheet 1 INVENTOR Ja cyues Jezger BY 72M ,Dm mmwm ATTO RN EYS Sept. 2, 1947. J. STEIGER 2,426,753

{CRANKSHAFT' FOR TWO-STROKE ENGINES .w'I'TH :TWELYE CYLINDERS in LINE 7 Fiied Sept. :5, 1945 :s Sheets-Sheet 2 JAc: cums $TRIGR I l I I,

Sept. 2, 1947. J. STEIGER 2,426,753-

CRANKSHAFT FOR TWO-STROKE ENGINES WITH TWELVE CYLINDERS IN LINE Filed Sept. 5, 1943 y a Sheet-Sheet s 1 V... a

a I v Q JACQUES STEIGER' Patented Sept. 2, 1947 'CBANKSHAFT FOR TWO-STROKE ENGINES WITH TWELVE CYLINDERS IN LINE Jacques Steiger, Winterthur, Switzerland, assignor to Sulzer Freres, Socit' Anonyme, Winterthur, Switzerland Application September 3, 1943, Serial No. 501,046 In Switzerland January 30, 1943 1 Claim. (01.- 74- 604) 7 The invention relates to a crankshaft for twostroke engines with 12 cylinders in line having a uniform cranksetting of 12 x 30 and is characterised in that the two halves of the crankshaft differ from eachother, that is to say the two halves of the crankshaft are not interchangeable and have the firing sequence of 1, 6, 11, 7, 3, 5, 10, 9, 2, 4, 12, 8, by means of which the critical speed of the 6th order is eliminated. In order to balance completely or in part the rotary moment of the 1st order of each crankshaft half, counterweights may be arranged on all the cranks.

Among known and possible crank orders in two-stroke engines with 12 cylinders in line, those with the twelve cranks all set at 30, an arrangement which gives the best balanced crank effort diagram, are the ones which come into consideration first of all. Selected from this number are those with perfectly balanced masses and without free forces and moments of the 1st and 2nd order; and the preference goes to those having small internal moments, as great moments in the case of long engines such as the twelvecylinder type might give rise to dangerous bending vibration.

In order to fulfil this latter requirement, each half of the engine must have its masses well balanced. The 6th order from the slipper pressures,

which come into consideration as exciters of tilting vibration about the shaft axis, needs to be balanced as Well as possible in each engine half, and this can be done with the known 30/ 90 displacing of the 120 three-pointed stars in each engine half. Further, adjacent cranks should be set at as wide an angle as possible to each other, so that the journals lying between them are relieved of centrifugal forces from the eccentric rotary masses of the working cranks and the lower sections of the connecting rods. In view of their great length, shafts with twelv cranks are usually divided at the centre, the two halves being in general made identical and interchangeable.

The fulfilment of all the above conditions reduces the favourable cranksettings to a very small number. Unfortunately, all of these cranksettings with the shaft in two identical and interchangeable halves carry with them the disadvantage of a dangerous critical speed of the 6th order in the neighbourhood of the normal working speed corresponding to the usual piston speeds, a circumstance which is inadmissibl in particular for propeller drives with variable speed. It would be possible to lower the critical speed by means of additional masses and elasticities, but this would bring also the stronger lower orders down into the neighbourhood of the service speed. The danger zone of the sixth order then remains in a somewhat lower speed range, which makes it necessary to install a vibration damper. I

An example of execution of the subject matter of the invention is represented diagrammatically in the accompanying drawings in which:

Figs. 1, 3 and 5 are diagrammatic views relative to a known form of crankshaft, Figs. 2, 4 and 6 are diagrammatic views relative to the improved form of crankshaft forming the subject matter of the present invention, Figs. 7, 8 and 9 are diagrams which will be more completely described hereinafter, Fig. 10 is anelevational view of a crankshaft embodying the present invention, Fig. 11 is an enlarged elevational view of the righthand half of the crankshaft shown in Fig. 10, Fig. 12 is an end view of the half of the crankshaft shown in Fig. 11, Fig. 13 is a view similar to Fig. 11 of the left-hand half of the crankshaft shown in Fig. 10, and Fig. 14 is an end View of the half of the crankshaft shown in Fig. 13.

Fig. 1 shows the cranksequence of a known form of execution with a regular arrangement of the 12 cranks at 30. and the firing order of 1, 6, 8, 10, 3, 5, 7, 12,2, 4, 9, 11. The two crankshaft halves are identical and interchangeable.

Fig. 3 illustrates the corresponding crank sequence of the 6th order with the cranks l, 2, 3, '1, 8, 9 turned upwards and cranks 4, 5, 6, 10, 11, 12 turned downwards.

Fig. 5 gives the corresponding vector diagram with the strong resultant harmonic force 6th order Rs.

Fig. '7 shows the computed form of the singlenode oscillation, which serves to determine the vector diagram according to Figs. 5 and 6. The cylinders 1-6 to the left of node K are reckoned positive, and 7-12 to the right of the nod negative. On account of the extremely favourable turning moment, twelve-cylinder engines with regular arrangement of the 12 cranks at 30 have light flywheels only, so that the oscillation node is in the neighbourhood of the centre of the engine.

Fig. 8 shows the distribution of the critical speeds and the height of the additional stresses T for the crank sequence according to Fig. 1 with the shaded, dangerous critical region of the 6th order in the proximity of the normal service 3 4 tional stresses, which would inevitably lead to the in each shaft half in the crank arrangement fracture of the crankshaft. This critical region chosen in Fig. 2. Counterweights on the cranks is eliminated by the present invention, as can .be also diminish or exclude the centrifugal forces seen from the further drawings. from the eccentrically rotating masses of the reversed. The 'two regular thr'ee-iiointed stars the 'neihb'ourinig, angleswith smalfintervening of each crankshaft section form the angle 30/ Q? angles.

as in Fig. 1, yet the two sections are different A physical embodiment of the crankshaft is and cannot be interchanged. shown" Figs. 10. ,to 14. The complete crank- Fig. 4 reproduces the crank isiequenc'e "of "the 'iS'h hqw j fin Fig. 10 and comprises a left- 6th order corresponding to F]; A 1, 2, 3, 10, 11, 12 turned rd'sa; 5, 6, '7, 8, 9, turned downwards.

Fig. 6 shows the new vector diagram, corre- 15 sponding to Figs. 2 and 4 andagaindrawn on 3.0 on center, and the cranks of the two halves the basis of the form of vibration, cbinpiitedace are-differently arra ged, an a ly, so that they cording to Fig. '7. The cylinders 1-6 to thejeft 16. e e a le. o the end Views of Figs. of the node are again given the positive eig'mena "an it will be noted that the er of the 7:12 .tg th right f t node'the negative sign. cranks consecutively around the axis of the or b qe her almost eseem'se erar k snart is thep diagrammatically indicated Zfaiiddescribedalioye Thosefigures a-lso thaytn annuiar"dis dsitienefthe eiafiks n half consecutively is 39 and "90 altern ti'v 1y, so that the ori isneeaer'zhe e'th RQman numerals.

I diaelra "A' er nksliaft fer: two'istroke fier cycle engines "hayin twelve cylinders line in which the e r gs consecutively around the axis of the "crankshaft unifofifiily are set at "on'*-c'enters,"'a grou of six consecutive cranks of a one en'dof i zxacefi 7 REFERENCES oiTEn ,wit y y a d alf A and a right-hand half B connected j 'ih c n'k s of each half are uniformly set at e 1 r u nt ally is eliminated, as described 7 ,en ne nasa Zbroad above eefange'between '70 claim;

"the era' kshafrbeing uifierent y eerangeu n 

